This invention relates to optical apparatus for the measurement of linear and angular displacements and more particularly to such apparatus capable of extreme accuracy, e.g., the measurement of angular orientation with sub-arcsecond precision.
Previously known optical shaft encoders, though capable of precision measurement under favorable conditions, are deficient in several respects. To minimize the various aberrations inherent in optical systems, the prior art devices, such as the Theodosyn, required complex optical systems comprising as many as thirty optical surfaces. Notwithstanding this use of multiple optical elements, these devices are still plagued with abberations. And not only are such complex optics very expensive, but equally important, proliferating optical elements increase the likelihood of precision degrading mechanical misalignments in a vibratory environment. In addition to complex optical arrangements, some known devices require multiple encoded discs for precision angle measurement, again adding to cost and complexity.
It is therefore an object of the present invention to provide an improved optical device capable of precisely measuring linear and angular displacements.
Another object is to provide such a device which employs a single encoded element and a virtually aberration free optical system having a single or a very few optical surfaces.
Yet a further object of the invention is to produce an optical measuring apparatus that is more highly stable and accurate than before known.
Other objects, features and advantages of the system will become apparent in what follows.